The objective of this project is to understand, in molecular terms, the structural organization and the functional operation of the reversible cycle of protein phosphorylation that mediates the intracellular actions of polypeptide hormones and growth factors. The polypeptides bind to glycoprotein receptors embedded in the cell membrane, triggering activation of a protein Tyr kinase intrinsic to the receptor. Oncogenes cause transformation of cells by producing proteins that have this type of kinase activity, presumably subverting the normal functioning of the phosphorylation cycle. The phosphorylation of intracellular proteins by polypeptide receptors or oncogene transforming protein kinases is reversed by the action of protein Tyr(P) phosphatases. The proposed research involves the purification and characterization of these phosphatases. Comparison of structural features will involve radioactive labeling and selective chemical modification prior to peptide mapping by high performance liquid chromatography (HPLC). Mapping will complement the determination and comparison of primary structure of the one peptide common to various phosphatases that contains a cysteine residue. Monospecific immunoglobulins will be employed in a "Western" immunoblotting procedure that will enable comparison of antigenic structures and detection of latent or inactive forms of the phosphatase. These structural features will be related to the functional properties of the phosphatases such as the pH optima, sensitivity to inhibitors, and substrate specificity using acidic and basic Tyr(P) proteins and peptides. The proposed research should provide new knowledge about these neglected phosphatases that are essential components of the system of cellular regulation, and potentially will reveal bases for novel therapeutic interventions in the action of the hormones and growth factors.